The objective of the research is to ascertain whether the size of mineral fibers such asbestos and fibrous glass is a determinant of the development of cancer as assayed by epithelial cell responses in vitro. Tracheal explants are maintained in chemically defined culture medium and fibers to be studied are added. Hyperplastic changes are noted and quantitated using image analysis equipment. The accuracy of hyperplasia induced in this culture system as a predictor of neoplasia is to be evaluated.